Most studies on
social capital and health are carried out with large home-based surveys, neglecting
that many interactions among individuals occur in the workplace. The objective
of this study was to explore the psychometric properties of a scale in Spanish
used to measure social capital at work. The scale designed by Kouvonen et al
was translated into Spanish and tested under classical test theory, item response
theory, and confirmatory factorial analysis; 152 public health workers from
different socio-cultural contexts participated in the survey. Internal consistency
was high (Chronbach's alpha = 0.88). Social capital at work correlated properly
with two Job Content Questionnaire dimensions. A ceiling effect was detected
and item difficulty was quantified. The confirmatory factor analysis showed
the expected theoretical components of social capital: bonding, bridging and
trust. The scale has acceptable psychometric properties, thus it can be used
in future studies.

Social capital
is considered an important determinant of individual and population health1.
Although there are several definitions of social capital, the most commonly
used in public health is Robert Putnam's one. He uses the concept to refer to
features of social organization which promote or improve the acquisition of
skills, agreements, trust and networks that facilitate social functioning to
achieve common goals2. This definition has allowed quantitative approximations
given that it can be related to indicators such as the level of trust, perceived
reciprocity and the density of membership to civic associations3.
Other definitions such as James Coleman and Pierre Bourdieu´s tend not
to be used in epidemiology since their approaches are more extensive and difficult
empirical operationalization. The first defines social capital in terms of its
role in the facilitation of individual or group action, while the latter emphasizes
the fungible nature of social capital within the political economy4.

Evidence from political
sciences indicates that communities with greater cohesion, by having greater
participation by civil society, tend to be more efficient in its operation,
creative in political initiatives, more successful in the implementation of
policies, and less corrupt2. The same review by Kawachi & Berkman
also reports observations from criminology that support this type of evidence,
by stating that societies with higher levels of organization tend to have less
crime and fewer suicides. Other studies have shown fewer behavioral problems
among minors and better economic and labor development in societies with greater
social capital2.

The vast majority
of studies conducted in developed countries suggest that social capital is part
of the causal mechanism whereby acts the income inequality on health ("income
inequality hypothesis")5; however, there is evidence that this does
not occur in other countries with lower level of economic development6,7.
In Latin America and the Caribbean, studies on the subject are still scarce
and tend to repeat the same findings observed in other developed countries8.
Perhaps the most relevant exception are the contrary effects described in the
studies where it seems to have a "perverse" connotation9-11; in other
words, with harmful effects on health.

Most epidemiological
studies on social capital have been carried out with general population using
large-scale surveys1,8. This has disregarded that much of the interactions
of individuals occur in working environments, which is why it is highly relevant
to assess social capital at work; in these contexts, important interactions
take place between peers and between leaders and subordinates, which may reflect
the general organization of society as a whole12. In addition, the
notion of social capital, recently has received greater attention as a possible
explanation to the disparities in health and its social gradient13.

A breakthrough
in this topic was the development in Finland of a short scale to measure social
capital at work14. This scale has the prospect of an inequality perspective
of the efficacy of social capital; with only eight items (table
1), it seeks to explore whether people feel respected, valued and treated
with equality at work. Theoretically, the scale incorporates cognitive (items
3, 5 and 8) and structural components of social capital (items 1, 2, 4, 6 and
7), it also incorporates the linking social capital (items 3, 4 and 5), the
bridging or relational social capital (items 6 and 7) and the bonding social
capital (items 1, 2 and 8)14. The cognitive component makes reference
to perceptions of support, reciprocity, exchange and confidence, while the structural
refers to the extent and intensity of the links. Another classification identifies
union social capital in relations among individuals of the same social group,
while it includes the bridging social capital to refer to connections between
people from different social groups14.

These dimensions
represent the core axes of social capital in the labor context, and therefore
the most representative indicators for its assessment, regardless of other cultural,
occupational or geographical aspects14. It is important to note that
the measurement of social capital in epidemiological studies tends to be one-dimensional
and based on relationships of trust and respect15,16, so this proposal
incorporates the key elements for an adequate measurement of social capital.

An initial assessment
of the scale, based on the classical test theory, was performed with the answers
given by Finnish workers in the public sector. The evaluation included validation
of appearance by an expert; internal consistency analysis; correlations between
items and the total score; convergence validity with procedural justice (Moorman's
scale)17, effort-reward imbalance (Siegrist's Effort-Reward Imbalance
scale)18, and Job control (Karasek's Job Content Questionnaire)19,
and divergence validity with anxiety traits (Trait Anxiety Inventory)20,
and the magnitude of changes at work (single question with values of one to
seven, interpreted as larger and more significant changes). The psychometric
results obtained during this analysis were satisfactory14.

The few studies
on social capital at work and health consistently show a positive effect, although
it should be noted that they all have been in countries with significant differences
in comparison with Latin America. For example, an ecological study in Russia
used the quality of relationships at work as an indicator of social capital.
This allowed identifying a relationship between social capital and life expectancy
and mortality21. Other data of the Saskatchewan working population
in Canada show that those who frequently socialized with coworkers tend to have
better health, compared with those who do not socialize22; something
similar was reported by Lindström et al. with Swedish workers. They used
participation in trade union meetings or study in labor circles as indicators
of social capital23.

In a multilevel
analysis, it could be shown that Finnish employees working in places with low
social capital tend to have more health problems, in contrast with those who
work in companies with high social capital24. Also in Finland, Liukkonen
et al. demonstrated that better self-reported health and less psychological
distress occur among workers who have a contract with job security and confidence
in the support of co-workers25. More recently, Suzuki et al. measured
social capital at work, through trust and reciprocity, in 1800 workers in 60
Japanese companies. Then, through a multi-level analysis, they explored the
effect of these indicators on the individual and enterprise. It was found that
only the level of corporate mistrust is associated with a greater likelihood
of individual smoking26.

All these studies
used different ways to measure social capital, which is a common trait in investigations
on the subject27. However, the need for a uniform vision of the construct
and its measurement remains an area of opportunity. One advantage of Kouvonen´s
model and scale is the fact that it incorporates the most important dimensions
of social capital in only a few items, and that regardless of culture they can
be considered universal dimensions, which led to the use of this scale in Latin
American populations. In this way, and given the need for standardized ways
to measure social capital, the objective of this work was to evaluate the psychometric
properties of a brief measurement scale of social capital at work. This seeks
to contribute to the achievement of a standard measure that allows future studies
to explore on key indicators of the level of social capital present in the workplace.

The psychometric
testing of the scale is part of a study on work characteristics of the health
services context and its impact on population health. In this context, it is
assumed that social capital and organizational characteristics are positively
associated with organizational performance, workers' health, and consequently
the health of individuals who receive their services28-30.

Materials and
methods

Participants
in the study. The study was performed in the municipalities of Guachochi
(Chihuahua), Jojutla (Morelos) and Tizimín (Yucatán), all in the
Mexican Republic, which were selected to incorporate the inherent variability
between the North, Center and South of Mexico. In each of these locations, workers
in the state health services or the Institute of social security and social
services for workers of the state were invited to participate. To collect the
data, managers were first contacted to explain the study in detail. Meetings
were then held with workers with the same objective, emphasizing that their
participation would be voluntary, anonymous, and without labor implications
for those who decide to answer the questionnaire or not. Informed consent with
signature from each participant was obtained. This study was approved by the
Ethics Committee of the National Institute of Public Health in Mexico.

Construction
of the scale in Spanish. Based on the original scale, an initial translation
into Spanish was done, and then back-translated into English to verify that
the content of the original scale was maintained31. Pilot tests were
conducted with 22 health professionals. This allowed modifying sentences to
make them understandable for individuals from the three participating regions.
The original and final items in English and Spanish, respectively, are found
in table 1.

Assessment
psychometric. Guidelines of the classical theory of test, confirmatory
factor analysis and item response theory were followed in order to elucidate
the psychometric properties of the scale. Classical theory considers that the
scores obtained by individuals have a component that reflects the magnitude
of the construct measured and an error component. Additionally, it assumes that
the true score corresponds to the mathematical expectation of the empirical
score, that the value of the real score of an individual is independent of the
score error, and that the errors of measurement in a test are independent of
errors in other tests32.

Firstly, an exploratory
factor analysis with the eight items was conducted, seeking to identify the
latent variables not observed and the structure foundation of the construct33;
in order to do this, an a-priori criterion was established to consider
that a factor was relevant if it presented a proportional contribution exceeding
5%. Then Cronbach's internal consistency was assessed. We explored the concurrent
validity through Spearman correlations among the scores obtained in the scale
and the dimensions of supervisor/boss social support and co-workers social support
from the job content questionnaire (JCQ)29, in its version validated
for Mexico34,35. This is one of the few validated scales in Mexico
related to the construct at issue. Analyses were done with the statistical program
Stata 11 (Stata Corporation, College Station, Texas).

Given that the
classical theory does not allow the comparison of a same construct scores obtained
with different instruments, and the inability to identify differences in the
difficulty of items and the skill of those who respond, among other limitations,
we carried out a follow-up assessment with some elements of the item response
theory. With this analysis, the difficulty of each item in relation to the ability
of people can evaluated. This facilitates the obtaining of total scores and
incorporating these features on a linear scale36. Moreover, among
other advantages, it can express parameters of items and people in the same
units, which allows to identify the items that an individual can resolve with
greater or lesser difficulty; it facilitates proper assessment even when there
is missing data, estimates the accuracy of measurement, and detects data that
do not conform to the model and outliers. From this approach, an efficient item
must follow a logistic curve in a manner that should only be properly answered
by individuals who possess the skills required by the cognitive demands intended
to be measured36.

Since on a Likert
scale, as the one evaluated here, a total score of the construct is obtained
by the sum of the scores obtained in each item, an initial exploration was carried
out with data from all workers using the Partial Credit Model37.
Under this model, the distances between the categories within the items are
not assumed as uniform. Data adjustment with the model was then estimated with
statistics of internal and external adjustment of workers and items, thus identifying
outliers that did not conform to the model. The quality of the instrument was
determined with criteria suggested by Fisher38. Curve characteristics
of each of the items were estimated. This allows looking at the relationship
between the candidates' level of skills and the probability of correct answer
to each item. All these analyses were undertaken with Winsteps TM39.

Lastly, taking
into consideration the information obtained in the previous analyses and conceptual
foundations of Kouvonen et al.'s scale, confirmatory factorial analyses were
done. This technique has shown its value to validate new questionnaires and
adaptations of questionnaires developed in other languages or implemented in
populations with different cultures40. The first model was made for
the single factor model (model 1) according to what was obtained in the exploratory
analysis; model 2 explored two factors (structural and cognitive components
of social capital) following the theoretical concepts referred by Kouvonen et
al14. Finally, a three factor model was assessed (linking, bridging
and bonding components of social capital). Schumacker & Lomax and Hair et
al.'s indexes and recommended values were used for the evaluation of adjustment41,42.
These analyses were done with use of the AMOS 4.01 program43.

Results

Information was
obtained from 152 health workers, most of them were women (62.8%), with ages
between 16 and 60 years (median = 34). The main activities of the participants
were nursing (38.16%), administrative (28.95%) and medicine (15.79%). Scores
according to their occupation can be seen in Figure 1, where
the similarity of scores is noticeable, however, with a tendency to be higher
among doctors. During factor analysis it was noted that a single factor, with
eigenvalue of 3.94, explained 94.13% of the variance. After a varimax
rotation, it was observed that factor loading greater than 0.65 were those for
items c3, c4, c5 and c7. After calculating the Kaiser-Meyer-Olkin measures of
sampling adequacy, values exceeding 0.80 were obtained for each item and in
overall, except for item c2 (0.78), which can be considered as "appropriate"44.
A Cronbach's alpha of 0.88 showed that all items have the same direction and
a high internal consistency.

Table
2 shows Spearman correlations with their respective 95% confidence intervals
between scores on the scale and dimensions of the JCQ. Social capital at work
positively correlated with the two dimensions of the JCQ that evaluate the level
of support provided by the boss (rho 0.66, p <0.01) and co-workers
(rho 0.54, p <0.01). The other dimensions showed several positive
correlations, as expected theoretically, but not with the same magnitude. These
findings suggest that there is a single construct that can be called social
capital at work, with an acceptable concurrent validity.

Item difficulty
was quantified by means of logit, obtained by multiplying the response odds
ratios to each item of the natural log. Thus it was observed that the easiest
item was c1 (- 0.51); followed in increasing order by items c2 (- 0.32), c8
(- 0.11), c4 (- 0.02), c7 (0.11), c3 (0.19), c5 (0.28), and c6 (0.37). This
is summarized in table 3. In the Wright map,
it was evident that workers have a much greater dispersion in skill to respond,
in comparison with the items (figure not shown). The three easiest items were
those part of the trust relationships component. In the same table, it can be
seen that the internal (infit) and external (outfit) adjustment statistics show
values between 0.8 and 1.3, which is evidence of an appropriate adjustment.

Finally, table
4 shows the adjustment indexes for the one-, two- and three-factor models,
using confirmatory factor analysis. The indexes were satisfactory in the three-factor
model (Figure 2), except for the evaluation using the x2 test, which could have been due to sample size45.

Discussion

This study presents
the results of several psychometric analyses on the Spanish version of Kouvonen
et al.'s social capital at work scale. The findings showed a good performance
of the scale in terms of classical theory. While globally acceptable performance
was observed from the item response theory, it also allowed identifying some
weaknesses in the scale. A ceiling-effect was evident in 8.55% of the participants,
which exceeds the expected (a maximum of 5% to be "acceptable")38,
and this thus suggests the need to have items that explore higher levels of
social capital at work and/or that workers responses were biased.

A differential
in the difficulty of items was also established, those related to trust (c1
and c2) being the easiest. While possible complementary items should seek the
incorporation of cognitive, structural, linking, bridging and bonding, it is
suggested that these latter ones are prioritized in terms of the construction
of items of greater difficulty. This should be explored in greater depth as
most of the epidemiological studies on social capital use measures based on
this type of indicators. If this is repeated in other types of populations,
it may be that the attempts to measure social capital have only partially explored
its effects. Model 3 shows the presence of dimensions of linking, bridging and
bonding of social capital with use of confirmatory factor analysis.

Some methodological
issues must be considered to adequately interpret the validity of the results.
The sample size can be considered small, however, this turns out to be sufficient
for the Rasch analysis, where it is well known that even in samples with less
than 150 individuals have more than 99% probability that the estimated value
of the difficulty of the item is not further than ± 1 logit of its stable
value46-49; something similar happens in the case of factor analysis,
where good estimates can be obtained when high commonalities are present50,
as seen in this study. In the case of confirmatory factor analysis, it is important
to remember that only the Tucker-Lewis index is independent of sample size51,
and good a index was obtained in this analysis. While acknowledging that a larger
sample would have allowed a more detailed assessment, all the findings suggest
that the sample size was sufficient to have a global scale psychometric assessment.

The results of
this study support the conclusion that we can rely on a short Spanish scale
which includes the components of linking, bridging and bonding, with acceptable
psychometric properties to measure social capital at work in contexts where
expected levels are not too high, or when aggregate indicators of a group are
intended, for example through medians, means or standard deviations. For social
epidemiology, organizational psychology, and occupational health, it is an important
step to have an efficient and consistent measurement method based solidly on
the theory. This was evaluated using elements of classical theory, confirmatory
factor analysis and Rasch method. The cross-cultural adaptation of this scale
integrated elements of three complementary approaches that allow greater validity
of the results of the analysis of the differential functioning of items40.

In conclusion,
this scale may be used in future studies with similar populations to the ones
studied here taking into account the aforementioned constraints. Experience
in this study allows us to point out that when there is a need to use an already-built-scale
in a different population or population, it is insufficient to rely on classical
test theory. It is advisable, and of low cost and simplicity, to make a more
detailed explorations of the psychometric properties by incorporating elements
of other psychometric approaches. The incorporation of the Rasch model and confirmatory
factor analysis for the psychometric assessment of complex constructs in public
health should become a regular practice, which will result in improving the
validity of its findings. Having a scale to measure social capital at work,
with acceptable psychometric results, will allow research in Spanish-speaking
countries on the subject to have greater validity of its findings.

Acknowledgements

The authors wish
to thank the directors of institutions and health workers that participated
in the study. This study was sponsored by the National Council of Science and
Technology - Conacyt, through Grant No. 87719 2008.